In the title compound, C29H27N3O5, the hydropyran ring adopts an envelope conformation with the methine C atom bearing the para-meth­oxy­benzene ring as the flap. The central pyrrolidine ring has a twist conformation on the N—C bond involving the spiro C atom. The piperidine ring adopts a chair conformation. An intra­molecular C—H⋯O contact closes an S(7) ring. In the crystal, inversion dimers linked by C—H⋯O inter­actions generate R22(18) loops and N—H⋯O hydrogen bonds connect the dimers into [100] chains.

As part of our ongoing studies of 4H-chromene derivatives (Devi et al., 2013), we have synthesized the title compound (Fig. 1) and report herein its crystal structure.

The hydropyrrolidine ring adopts an envelope conformation, the piperidine ring adopts a chair conformation and the pyran ring adopts an envelope conformation. The pyrrolidine ring (N2/C9/C10/C17/C22) makes a dihedral angle of 86.78 (8)° with the other pyrrolidine ring (N3/C22/C23/C28/C29) which shows that they are almost orthogonal to each other. The pyrrolidine ring makes a dihedral angle of 29.65 (8)° with the pyran ring (O2/C8-C11/C16), it makes a dihedral angle of 8.88 (9)° with the piperidine ring (N2/C17-C21).

The other pyrrolidine ring (N3/C22/C23/C28/C29) makes a dihedral angle of 71.63 (8)° with the pyran ring, it makes a dihedral angle of 86.84 (8)° with the piperidine ring which shows that they are almost at right angles to each other. The dihedral angle between the pyran ring and the piperidine ring is 30.34 (8)° . The oxygen atom O5 attached with pyrrolidine ring deviates by -0.0200 (1)Å. The nitrogroup attached with the pyrrolidine ring makes a diherdal angle of 88.83 (1)° which shows it is in orthogonal orientation . The crystal packing features N—H···O, C—H···O hydrogen bonds and intramolecular C—H···O hydrogen bonds.

To a solution of isatin (1equiv) and piperidine-2-carboxylic acid (1.4 equiv) in dry toluene, was added 2-(4-methoxyphenyl)-3-nitro-2H-chromene (1equiv) under nitrogen atmosphere. The reaction mixture was refluxed for 24h in Dean-Stark apparatus to give the cycloadducts. After completion of the reaction as indicated by TLC, the solvent was evaporated under reduced pressure. The crude product was extracted with dichloromethane. The organic layer was dried with anhydrous sodium sulphate and concentrated in vacuo. Then the crude product was purified by column chromatography using hexane/EtOAc (7:3) as eluent. Colourless blocks were obtained by slow evaporation of a solution of the title compound in ethyl acetate at room temperature.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Acknowledgements

The authors thank the TBI X-ray facility, CAS in Crystallography and Biophysics, University of Madras, India, for the data collection. SK,TS and DV thank the UGC (SAP–CAS) for the departmental facilties. SK also thanks DST PURSE for a Junior Research Fellowship and TS also thanks DST Inspire for a fellowship.

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